The invention relates to a deformation sensor for a safety device.
Passive safety devices which are triggered in the event of an accident without the assistance of the vehicle occupants have been known for a very long time. For example, airbag systems have been installed as standard equipment in motor vehicles in which an air cushion is inflated automatically when the vehicle collides with an obstacle. The aim is also to arrange airbag systems on vehicle side walls or vehicle doors, in order to improve the protection of the vehicle occupants in the event of a side-on collision of the vehicle. Ideally, the side airbag has a relatively large volume in the inflated and deployed state and extends over the entire height of the side wall or door and covers a window aperture.
Since motor vehicles have only minimal collapsible zones in the side region which can absorb some of the collision energy, the timespan available for bringing the side airbag into a state effective for protection is very much shorter than in the case of a front collision.
German Patent Document DOS 3,716,168 describes a deformation sensor which is arranged directly under the shell in the side region of the vehicle and which extends over the entire width of a door. The deformation sensor is composed of two pressure-sensitive signal elements which are arranged a short distance one behind the other and which, in the event of a deformation of predetermined intensity, transmit an electrical signal to an evaluation circuit. The evaluation circuit checks the time sequence of the transmitted signals and, if the sequence is correct and other preconditions regarding intensity and duration are satisfied, triggers the safety device. The time interval between the first signal and the signal of the second signal element depends on the distance in space between the two signal elements and on the speed with which an obstacle dents the motor vehicle. This criterion for the deformation speed makes it possible, with restriction, to conclude that there is imminent danger for the occupants, and therefore, when a critical deformation speed is exceeded, the safety device is triggered. This avoids an unnecessary triggering of the safety device when an obstacle deforms the shell of the vehicle very slowly.
In order to avoid the outlay and weight of an additional supporting profile, the known deformation sensors are preferably used in conjunction with an already existing reinforcing profile, as is also known from EP 0,518,381 A1. Since the latter should run close under the shell, there is very little constructional space available. The disadvantage of this is that the deformation speed is determined inaccurately, since the deformation travel taken as a basis is very small, and, furthermore, the mounting or exchange of the deformation sensor is complicated and therefore costly.
One possibility of avoiding the constraint of the available constructional space is to integrate the first (outer) signal element into a protective strip mounted on the outside of the shell of the vehicle and to mount an inner signal element on the shell from inside at a specific distance from a reinforcing profile, as is known from German Patent Document DE 4,241,382 A1. The shell at the same time forms a sufficiently rigid support for the outer signal element. According to the publication mentioned, a deformation occurs only after electrical contact is made in the outer signal element. Subsequently, with an increasing deformation of the shell, the inner signal element moves in the direction of the reinforcing profile and, after a time span dependent on the deformation speed, comes to bear on the reinforcing profile, thereby causing contact to be made in the inner signal element. A disadvantage of this arrangement is that the distance between the shell and the reinforcing profile is constant over the door width and determined exactly only in very rare instances. Consequently, only imprecise information regarding the deformation speed can be obtained from the recorded time span.
Furthermore, German Patent Documents DE 2,212,190 A1 and DE 2,149,158 B2 disclose a deformation sensor in which the two signal elements are integrated into the protective strip. Both known sensors are designed so that their response thresholds are below the force which leads to a deformation of the shell. This is a serious disadvantage, particularly in use for triggering an airbag where a high response threshold is desired in order to avoid faulty triggerings.
Am object of the invention is to provide a deformation sensor of the generic type which avoids the disadvantages of the known deformation sensor.
This object is achieved by a deformation sensor for a safety device for the protection of vehicle occupants against a side-on collision, which is composed of at least one pressure-sensitive signal element and which is arranged in a side region of the motor vehicle, at least one signal element being integrated into a protective strip mounted on an outside surface of the shell of the vehicle, the protective strip having integrated signal elements forming an elongate sectional bearer which can be compressed by a perpendicular force effect exceeding a specific threshold, with the result that the signal elements respond, wherein a predetermined threshold of the signal element is so high that, in the event of a perpendicular force effect on the protective strip, the shell is deformed, without a signal element being triggered, until a reinforcing profile arranged behind the shell opposes a further deformation of the shell, whereupon at least one signal element is loaded with pressure and responds.
During assembly, the signal elements, integrated according to the invention into the protective strip, are mounted together with the protective strip in one operation, while the connecting leads can be guided through the shell into the interior of the door through lead tunnels provided specifically for this purpose. In the event of a defect of a signal element, the entire protective strip is exchanged with little labor being involved. A further advantage is that the signal elements are welded in within the protective strip in an air-tight and water-tight manner and can consequently be protected against environmental influences in the best possible way, thereby improving the lifetime and reliable functioning of the signal elements. Moreover, the deformation sensor according to the invention requires no additional carrier or constructional elements increasing the weight of the vehicle, but makes use of already existing elements.
Advantageous embodiments and developments of the deformation sensor according to the invention are described herein. Thus, in the developments, provision is made, analogously to the deformation sensor described in German Patent Document DOS 3,716,168, for arranging two signal elements one behind the other in parallel, while one signal element or both can be accommodated in the protective strip. The determination of the deformation speed thereby becomes more accurate, since the distance between the signal elements arranged one behind the other is comparatively large and is predetermined very precisely.